1. Field of the Invention
The present invention relates to a semiconductor device, such as a MEMS (Micro Electro Mechanical System) acceleration sensor, which is manufactured from a semiconductor substrate, and to a method of manufacturing and inspection thereof.
2. Description of the Related Art
FIGS. 1A through 1D show a conventional acceleration sensor. This acceleration sensor includes a substrate 10 having sensor circuits (not shown) mounted thereon and is integrally formed from a silicon wafer by using a semiconductor manufacturing technique. As shown in FIG. 1A and FIG. 1B, the substrate 10 includes four generally rectangular contoured grooves 11a through 11d each having a groove width. A spindle portion 12 is formed in the central region of the substrate. A quadrangular frame portion 13 is formed to surround a circumference of the spindle portion 12. Four brace portions 14 are bendable so as to act as a bendable cantilever. The substrate 10 has such a structure that four bendable brace portions 14 connect the spindle portion 12 to the frame portion 13 while spindle portion 12 is movable against the frame portion 13. A stress detecting sensor using a piezo electric element, etc. and a circuit such as wiring (not shown) are formed on a surface of each of the brace portions 14. In addition, the frame portion 13 has a length “A” of approximately 2 mm on a side and a height “B” of approximately 500 μm. Furthermore, a thickness of each of the brace portions 14 is approximately 10 μm.
This accelerator sensor is generally manufactured as follows. First, as is the case with conventional LSIs, a plurality of sensors, wiring and electrodes for external connection and others are formed on a front surface of the silicon wafer. Parts of the silicon wafer, which correspond to a region located between the spindle portion 12 and the frame portion 13, are then removed by etching so as to form the grooves 11a through 11d while leaving the brace portion 14. This etching is conducted on the front surface side. An etching depth is adjusted to be substantially equal to a thickness of the brace portion 14.
After the etching on the front surface side, the silicon wafer is flipped vertically. Parts of the silicon wafer, which correspond to a region located between the spindle portion 12 and the frame portion 13, are then removed by etching so as to form the grooves 11a through 11d in the rear surface side. This etching is conducted until the brace portions 14 remain, each having a given thickness and other parts of the silicon are removed to the depth of the parts etched in a surface side etching.
As a result, parts located between the spindle portion 12 and the frame portion 13 are removed to form the grooves 11a through 11d. Four brace portions 14 connect the spindle portion 12 to the frame portion 13. An accelerator sensor shown in FIGS. 1A through 1D is thereby obtained.
The accelerator sensor shown in FIGS. 1A through 1D is to be accommodated within a package. Electric wiring is provided for connecting the sensor circuits to an external connecting terminal outside of the package. As the four brace portions 14 connect the spindle portion 12 to the frame portion 13, in this accelerator sensor, the spindle portion 12 is displaced with respect to the frame portion 13 because of the bending of the brace portions 14 when acceleration is applied to the accelerator sensor. Bending magnitudes of the four brace portions 14 depend on the magnitude and direction of the applied acceleration. As bending sensors, such as the piezo electric elements are respectively provided on the brace portions 14, the magnitude and direction of the applied acceleration can be calculated on the basis of magnitudes of the bending of brace portions 14.
However, the above-mentioned accelerator sensor encounters the following problem. To leave the brace portions 14 which connect the spindle portion 12 to the frame portion 13, and separate the spindle portion 12 from the frame portion 13 by removing parts of a silicon wafer other than the brace portions 14, there is a necessity to conduct etching on both of the front surface side and the rear surface side. Therefore, after completion of etching, there is a necessity to inspect whether an offset between etching patterns in the front surface side and the rear surface side is within an acceptable tolerance in magnitude or not. It is to be noted that a large amount of displacement causes some defects, such as degradation of a sensor characteristic.
For an accurate measurement of the displacement or offset that exists between the grooves 11a through 11d forming a front surface pattern and the grooves 11a through 11d forming a rear surface pattern, one can typically use an apparatus which enables simultaneous inspection of a processed front surface and a processed rear surface of a substrate. In addition, one can use a method of inspecting the substrate by using an infrared microscope which shows through the substrate, in one surface. However, a particular apparatus is needed in each case. For this reason, an accurate inspection of the displacement can not be expected through an appearance check by using a typical metallographic microscope. There was therefore a possibility that defective products flew out.
An object of the present invention is to provide a semiconductor device which can be readily inspected for a displacement existing between grooves formed along a front surface pattern and grooves formed along a rear surface pattern, without using any special apparatus.